High Throughput Quantum Efficiency Combinatorial Characterization Tool and Method for Combinatorial Solar Test Substrates

ABSTRACT

Simultaneous measurement of an internal quantum efficiency and an external quantum efficiency of a solar cell using an emitter that emits light; a three-way beam splitter that splits the light into solar cell light and reference light, wherein the solar cell light strikes the solar cell; a reference detector that detects the reference light; a reflectance detector that detects reflectance light, wherein the reflectance light comprises a portion of the solar cell light reflected off the solar cell; a source meter operatively coupled to the solar cell; a multiplexer operatively coupled to the solar cell, the reference detector, and the reflectance detector; and a computing device that simultaneously computes the internal quantum efficiency and the external quantum efficiency of the solar cell.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/334,165, filed May 12, 2010 and entitled “High ThroughputCombinatorial Characterization Tool for Combinatorial Solar TestSubstrates,” the contents of which, in its entirety, is hereinincorporated by reference.

BACKGROUND

1. Technical Field

The embodiments herein generally relate to solar processing andcharacterization, and more specifically, to a high throughputcombinatorial characterization tool for combinatorial test substrates.

2. Description of the Related Art

Some exemplary solar processing operations include operations for adding(depositions) and removing layers (etch), defining features, preparinglayers (e.g., cleans), doping, etc. However, solar companies conductresearch and development (R&D) on full substrate processing, often onvery large substrates and requiring a complete solar cell manufacturingline. This approach has resulted in high R&D costs and the inability toconduct extensive experimentation in a timely and cost effective manner.Combinatorial processing as applied to solar manufacturing operationsenables multiple experiments to be performed on a single substrate andwithout a complete solar cell manufacturing line. Equipment forperforming the combinatorial processing and characterization of thecombinatorial test substrates must support the efficiency offeredthrough the combinatorial processing operations.

Combinatorial processing enables rapid evaluation of solar processingoperations. The systems supporting the combinatorial processing areflexible to accommodate the demands for running the different processeseither in parallel, serial, or some combination of the two. A valuablecomponent of the systems for combinatorial processing are thecharacterization tools used to produce the data from high throughputexperimentation in such a way that the process does not slow down. Highperformance combinatorial characterization tools are needed to quicklyprocess and characterize the combinatorial test substrates.

Conventional solar electrical characterization such as internal quantumefficiency and external quantum efficiency measurements in a R&Denvironment is performed independently of one another in a manual andsequential mode. However, the conventional process tends to be timeconsuming and resource demanding resulting in a significant loss intesting throughput. For example, when there is a need for measuringmultiple sites per sample, the throughput and resources of the operatorsbecomes a critical issue. Taking 32 sites per sample as an example, ittakes 30 minutes to measure the external quantum efficiency (EQE) persite. To finish the characterization of each example, the operator hasto move the sites every 30 minutes for the next 16 hours. It is alengthy and tiring test.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the followingdetailed description with reference to the drawings, in which:

FIG. 1 illustrates a schematic diagram of a combinatorial screeningprocess according to an embodiment herein;

FIG. 2A illustrates a block diagram of a quantum efficiency apparatusaccording to an embodiment herein;

FIG. 2B illustrates a schematic diagram of a quantum efficiencymeasurement tool according to an embodiment herein;

FIG. 2C illustrates a graphical representation of an output curve of aquantum efficiency measurement tool according to an embodiment herein;

FIG. 2D illustrates a schematic diagram of the rotation of anarticulation platform of a quantum efficiency measurement tool accordingto an embodiment herein;

FIG. 3A illustrates a schematic diagram of an unloaded sample trayaccording to an embodiment herein;

FIG. 3B illustrates a schematic diagram of a loaded sample trayaccording to an embodiment herein;

FIG. 4A illustrates a block diagram of an X-Y control device accordingto an embodiment herein;

FIG. 4B illustrates a block diagram of a multi-pin combinatorialcharacterization apparatus according to an embodiment herein;

FIG. 4C illustrates a block diagram of a Z-stage combinatorialcharacterization apparatus according to an embodiment herein;

FIG. 4D illustrates a block diagram of a Z-stage combinatorialcharacterization apparatus in transition according to an embodimentherein;

FIG. 4E illustrates a view of a probe fixture according to an embodimentherein;

FIG. 5 illustrates a flowchart of a method according to an embodimentherein; and

FIG. 6 illustrates a computing system according to an embodiment herein.

DETAILED DESCRIPTION OF THE DRAWINGS

The embodiments herein and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. The examples used hereinare intended merely to facilitate an understanding of ways in which theembodiments herein may be practiced and to further enable those of skillin the art to practice the embodiments herein. Accordingly, the examplesshould not be construed as limiting the scope of the embodiments herein.

With increasing energy demands, alternative (e.g., green) energy gainsmore and more attention. As an important part of the research anddevelopment of solar cells, the electrical characterization of thosesolar cells also needs to improve. Measurement of the quantum efficiencyof a solar cell is a valuable parameter to judge the cell performance.It determines how efficiently the solar energy can be converted intoelectricity. Quantum efficiency may be characterized by measuring thecurrent-voltage (I-V) curve of the cell under standard one sunillumination. In the lab test environment, a solar simulator is used asthe light source with less than 1% spectrum difference as actualsunshine. The current generated by an illuminated solar cell is measuredas the voltage scan by connecting the electrodes of the cell to a sourcemeter.

The embodiments herein provide a high performance combinatorialcharacterization tool that saves both operator resources as well as testtime, and offers a key function for high throughput and combinatorialresearch. Referring now to the drawings, and more particularly to FIGS.1 through 6, where similar reference characters denote correspondingfeatures consistently throughout the figures, there are shown severalembodiments.

Combinatorial processing systems are only as good as thecharacterization available. Therefore, the high performancecharacterization tool described herein provides the means by which truehigh throughput experimentation may be accomplished. The operator burdencan be minimized by test automation. The test time can be significantlyreduced by parallel testing by measuring multiple sites at the same timeinstead of measuring one at a time. Although the high performancecharacterization tool described herein exhibits extraordinary utility inthe field of combinatorial processing (e.g., by enabling high throughputexperimentation), the embodiments herein, however, are not limited tocombinatorial processing. Thus, the use of the high performancecharacterization tool described herein in combinatorial processingsystems represents one of many valuable applications of the embodimentsherein. For example, traditional solar cell experimentation andexploration methods, semiconductor manufacturing and fabrication, lightemitting diode (LED) applications, flat panel display applications,characterization of photochromic materials, characterization ofelectrochromic materials, and characterization of thermochromicmaterials, among other applications, would all benefit from the highthroughput and rapid characterization offered by the high performancecharacterization tool described herein.

As described above, during one embodiment of combinatorial processing,each wafer is subjected to many different process conditions. FIG. 1illustrates an example of such a combinatorial screening process. Asshown in FIG. 1, combinatorial screening process 100 includes primaryscreening process (110), secondary screening process (120), and tertiaryscreening process (130). In FIG. 1, for example, numerous materialcompositions (e.g., 18 spots or 46 spots on a single wafer, where eachspot is a unique material composition) are systematically explored on asingle wafer during an initial primary screening process (110) at speedsthat would otherwise be impossible using traditional methods and tools.In other words, in the embodiment shown in FIG. 1, primary screeningprocess (110) is an initial screening that processes many samples torule out materials for further screening. Once the best materials,process conditions, or process integration are identified using initialcombinatorial screening methods (e.g., during primary screening process(110)), that material is then scaled up to test the performance (e.g.,EQE and IQE performance) of that material and/or conditions during asecondary screening stage (e.g., secondary screening process (120)).Furthermore, according to one embodiment herein, additional testing maytake place during tertiary screening process (130). During tertiaryscreening process (130), for example, the materials and/or processconditions that were not filtered out during primary screening process(110) and secondary screening process (120) are scaled up to afull-scale device size. Furthermore, due to the speed andnon-destructiveness of the performance test (described in further detailbelow) occurring in secondary screening process (120), materials and/orconditions that pass both the primary screening process (110) andsecondary screening process (120) can rapidly proceed to tertiaryscreening process (130). Consequently, to test the performance of thesematerial compositions, embodiments herein utilize an improvedmeasurement tool to enable the collection of information more rapidly.

FIG. 2A, with reference to FIG. 1, illustrates a block diagram ofquantum efficiency apparatus 1 according an embodiment herein. Inquantum efficiency apparatus 1, the light spectrum is filtered so thateach wavelength of light can be used individually to test theperformance of solar cells 42, and in one particular embodiment, thesolar cells 42 may be individual site-isolated devices on acombinatorial solar test substrate 40 where each of the site-isolateddevices has been varied as compared to one another. In alternateembodiments, the substrate 40 being tested may be a substrate 40 havingmultiple unvaried solar cells 42 produced for either commercial orresearch and development purposes. For purposes of discussion only,examples of a solar test substrate 40 include, but are not limited to:copper indium gallium diselenide (CIGS), copper zinc tin sulfide (CZTS),and other thin film photovoltaic (TFPV) materials with a silicon orglass substrate. Quantum efficiency apparatus 1 measures the reflectedlight and the transmittance of the light simultaneously in order todetermine the amount of light absorbed and converted into electricity bythe solar cells 42 in the site-isolated regions. In other words, quantumefficiency apparatus 1 simultaneously measures internal quantumefficiency (IQE) and external quantum efficiency (EQE). EQE iscalculated as the ratio of a measured number of charge carriers (e.g.,current) collected by a solar cell 42 to the number of photons of agiven energy shining on the solar cell 42 from outside (i.e., incidentphotons). IQE is calculated as the ratio of the number of chargecarriers (e.g., current) collected by the solar cell 42 to the number ofphotons of a given energy that shine on the solar cell 42 from outsideand is absorbed by the solar cell 42.

As shown in FIG. 2A, one embodiment of quantum efficiency apparatus 1includes a quartz tungsten halogen (QTH) lamp 5 (e.g., 1000 W FEL QTHlamp available from Newport Corporation, Irvine, Calif., USA), a filterwheel 10, an optical chopper 15, a monochromator 20, a three-way beamsplitter 25, a reflectance detector 30, a reference detector 35, asubstrate 40 (which may include one or more solar cells 42 as aspecially treated region thereon, as described below), a white lightbiased controller 45, a sample tray 50, a source meter 55, a multiplexer60, a lock-in amplifier 65, and a computing device 70. As discussed infurther detail below, by using a three-way beam splitter 25, quantumefficiency apparatus 1 measures both incident and reflected lightintensity to calculate EQE and IQE simultaneously. Therefore, incontrast with conventional devices, quantum efficiency apparatus 1 doesnot require a user to remove a sample to obtain a reference lightmeasurement, and quantum efficiency apparatus 1 is able to collect IQEwithout making any special adjustments to the apparatus 1 and taking asecond measurement. Additionally, no adjustments to data obtained fromreflectance detector 30 and source meter 55 have to be made because allof the necessary data is collected on quantum efficiency apparatus 1 andthe measurements of absorbance and reflectance are made at the same timeusing computing device 70. Moreover, simultaneous EQE and IQEmeasurements performed by quantum efficiency apparatus 1 provideimproved accuracy over conventional systems by eliminating errors,complication, time, materials, and cost associated with moving a samplefrom one measuring device to another measuring device.

According to the embodiment shown in FIG. 2A, the combination of QTHlamp 5, filter wheel 10, optical chopper 15, and monochromator 20produces light 20 a at a specific wavelength, to allow precisesimultaneous measurement of the EQE and IQE characteristics of solarcell 42. Light 20 a is directed to three-way beam splitter 25, where onehalf of the incoming light is directed to a solar cell 42 within asubstrate 40 (e.g., light 25 a) and the other half of the incoming lightis directed to reference detector 35 (i.e., light 25 b). When light 25 ahits solar cell 42 (e.g., a CIGS, CZTS substrate, etc.), the reflectedlight (i.e., light 40 a) is directed by three-way beam splitter 25 toreflectance detector 30 (i.e., in the form of light 40 b). The amount oflight 25 a absorbed by the solar cell 42 within the substrate 40 andconverted to an electrical current is detected by source meter 55 thatis coupled to pins 113 that are in contact with the solar cell 42 and/orsubstrate 40 (as discussed in further detail below). In addition,according to one embodiment herein, white light bias controller 45 isused to isolate the EQE and IQE response from a single absorption layer(not shown) in solar cell 42 when solar cell 42 is a multi-layerabsorption cell by biasing a single layer in solar cell 42 to whitelight (e.g., natural light).

As further shown in FIG. 2A, light 25 b is directed to referencedetector 35 and the output of reference detector 35 serves as an inputto multiplexer 60. Multiplexer 60 accepts, as input, the output ofreflectance detector 30 and the current produced by solar cell 42.Thereafter, lock-in amplifier 65 extracts and amplifies the specificwavelength desired to calculate the EQE and IQE characteristics of solarcell 42 from the inputs of multiplexer 60.

By measuring the incoming light 20 a (via reference detector 35) foreach test (e.g., through multiplexer 60), the accuracy of the resultingdata is increased because the light source intensity and wavelength isdetermined (e.g., on computing device 70) at the same time as theabsorbed light (e.g., from solar cell 42) and the reflected light (e.g.,from reflectance detector 30) for each solar cell 42 on substrate 40. Inaddition, computing device 70 may include elements described in FIG. 6,and further described below, in order to perform its calculations andprocessing. In contrast to a traditional testing method, where theincoming light is only tested at the beginning before conducting a teston the entire substrate, quantum efficiency apparatus 1 tests incominglight (e.g., light 20 a) of each solar cell 42 on substrate 40 at thesame time as the other light measurements (absorbance and reflectance).Using reference detector 35 allows quantum efficiency apparatus 1 toidentify any drift in the wavelength between tests of each solar cell42. Moreover, using reference detector 35 improves the accuracy of themeasurements and further improves the uniformity and accuracy of testingmultiple solar cells 42 (e.g., on substrate 40 during combinatorialtesting, testing multiple solar cells 42 on multiple substrates 40, andother testing scenarios that involve multiple solar cells 42).

FIG. 2B, with reference to FIGS. 1 and 2A, illustrates a schematicdiagram of a quantum efficiency measurement tool 80 according to anembodiment herein. As shown in FIG. 2B, quantum efficiency measurementtool 80 includes three-way beam splitter 25, reflectance detector 30,reference detector 35, substrate 40, sample tray 50, light enclosure 90,emitter 92, support platform 94, articulation platform 96, probe module97, and transmittance detector 98. Also shown in FIG. 2B is light 25 a,which is light originating from emitter 92 after traveling through lightenclosure 90 and being split at three-way beam splitter 25. In oneembodiment the light 25 a coming from the emitter 92 may have allwavelengths of natural sunlight for the testing of solar cells 42. Thespectrum of light frequencies of light 25 a may be varied depending onthe samples being tested, for example there may be applications whereinfrared or ultraviolet wavelengths may be needed. In one embodiment,emitter 92 also includes QTH lamp 5, filter wheel 10, chopper 15, andmonochromator 20 (shown in FIG. 2A). In FIG. 2B, light 25 a comprises afocused beam of light from emitter 92 that has been filtered to onewavelength (e.g., via filter wheel 10, shown in FIG. 2A) as is directedover a specific spot on substrate 40 (e.g., on solar cell 42). Thefocused beam of light covers an area within the solar cell 42 beingtested that is smaller than the area of the solar cell 42. Such a smalllocalized beam of light ensures that all of the light hits theparticular solar cell 42 being tested and that the beam of light is notaffecting neighboring cells. This small localized beam of light withinthe solar cell 42 improves the consistency of the measurements betweendifferent solar cells, which may be valuable when comparing data forcombinatorially varied solar cells 42 on a single substrate 40 or evenon different substrates. To measure the QE of each of the solar cells42, the filter wheel 10 cycles the beam of light through all of thewavelengths of light coming from emitter 92 and which, in the example ofa solar cell 42, will be wavelengths in the spectrum of naturalsunlight. The electrical current produced by the solar cell 42 at eachof the wavelengths is measured along via probe module 97 (e.g., usingpins 113 shown in FIG. 2A) with the reflected light to determine thequantum efficiency at each of the wavelengths. A set of curves, such asthe one illustrated in FIG. 2C, may be generated using this data. Asshown in FIG. 2C, the results of four different testconfigurations/samples are depicted in order to compare the quantumefficiency percentage versus the wavelength for each sample. Differentconfigurations/samples generate different results based on theparticular configuration/sample. According to the embodiments herein,the most desirable configuration/sample is the one with the greatestquantum efficiency percentage, which in FIG. 2C, is the top-most curve.In the embodiment shown in FIG. 2B, sample tray 50 is located at a fixeddistance (e.g., approximately 2-5 inches) from three-way beam splitter25. As described in further detail below, articulation platform 96 movessample tray 50 along two axes to enable positioning of each solar cell42 on the substrate/coupon 40 under the focused light beam whilemaintaining a fixed distance from three-way splitter 25.

Quantum efficiency measurement tool 80 may further include atransmittance detector 98 (along with probe module 97) on articulationplatform 96 and under sample tray 50 to measure the transmittance of athin film glass solar cell 42 on substrate 40 or the efficiency of anelectrochromic material in another potential use of this tool 80 wheremultiple electrochromic materials are deposited and varied from oneanother on a combinatorial test substrate 40. In such an embodiment,articulation platform 96 rotates (e.g., as shown in FIG. 2D) to alignthe transmittance detector 98 under solar cell 42 on substrate 40 andthree-way beam splitter 25. Transmittance is useful, for example, whendeveloping electrochromic materials and therefore there is a need toshine light 25 a through the substrate 40 to measure the transmittanceof the electrochromic material.

FIG. 3A, with reference to FIGS. 1 through 2D, illustrates a schematicdiagram of an unloaded sample tray 50 according to an embodiment herein.In addition, FIG. 3B, with reference to FIGS. 1 through 3A, illustratesa schematic diagram of a loaded sample tray 50 according to anembodiment herein. As shown in the embodiment of FIGS. 3A and 3B, sampletray 50 includes a support frame 82 to hold a solar cell substrate 40,where substrate 40 may include one solar cell 42 or multiple solar cells42. According to one embodiment herein, when there are multiple solarcells 42 on substrate 40, each solar cell 42 is combinatorially varied.Substrate 40 is held in place by clamp 84, where clamp 84 is secured viachannels 86. The channels 86 may be configured as a lip/ledge on whichthe substrate 40 rests, or the channels 86 may include vacuum-likeproperties to further retain the substrate 40 thereon. Operativelyconnected to support frame 82 are sample guides 88 a, 88 b, which areperpendicularly coupled to each other. In addition, while not shown inFIGS. 3A and 3B, in one embodiment, the sample tray 50 may betemperature controlled to regulate the temperature of the substrate 40being tested. Substrate 40 is secured to the support frame 82 bypositioning the substrate 40 at a corner 85 of the channels 86. Thesample guide 88 a moves axially and translationally with respect tosample guide 88 b and the support frame 82 to accommodate differentsizes of substrate 40. Once positioned on the sample guide 88 a andaligned in the channel 86, the substrate 40 is locked in place with theclamp 84, which, in one embodiment, may use a vacuum (not shown) tofurther retain the substrate 40 in place.

FIG. 4A, with reference to FIGS. 1 through 3B, illustrates a blockdiagram of a multi-axis (e.g., X-Y) control device 101 according to anembodiment herein. The embodiments, as described herein, utilize the X,Y, and Z axes to define various geometric planes associated with thecomponents described herein. Those skilled in the art would recognizethat the X, Y, and Z axes may be configured in any suitable orientation,and the embodiments herein are not restricted to any particularorientation. As shown in FIG. 4A, X-Y control device 101 includes anX-axis articulator 102 (e.g., a step motor), a Y-axis articulator 104(e.g., a step motor), an X-axis controller (e.g., SMC100CC controlleravailable from Newport Corporation, Irvine, Calif., USA), an optionalremote controller 106 a, a Y-axis controller (e.g., SMC100CC controlleravailable from Newport Corporation, Irvine, Calif., USA), an optionalremote controller 108 a, a power supply 111, a pneumatic solenoid 112,and a solenoid power supply 114. According to one embodiment herein,remote controllers 106 a and 108 a are operatively coupled to a remoteserver 107 to allow remote control and automation of X-axis controller106 and Y-axis controller 108, respectively. In addition, according toone embodiment herein, pneumatic solenoid 112 is coupled to a pluralityof pins 113, which articulate in the Z-direction (via pneumatic solenoid112) to form electrical connections to substrate 40 on articulationplatform 96. The pins 113 may be configured as push-pins that include aspring at the tip to press against the electrodes of the substrate 40,or they may be sharp tipped stiff pins, or any other type of suitableprobe. As shown in FIG. 4A, pneumatic solenoid 112 as well as X-axiscontroller 106 and Y-axis controller 108 are coupled to power supplies(i.e., power supply 111). While shown in FIG. 4A as one power supply111, embodiments herein are not limited to such a configuration andthose of ordinary skill in the art could provide a separate power supplyconnected to each of the X-axis controller 106 and Y-axis controller108, respectively. Furthermore, power supply 111 and power supply 114could also be consolidated into a single power supply unit to providepower to the X-axis controller 106, Y-axis controller 108, and pneumaticsolenoid 112.

Moreover, according to one embodiment herein, X-Y control device 101 isoperatively coupled to articulation platform 96 and sample tray 50 inorder to move tray 50 (shown in FIG. 2B) along an X-axis and/or along aY-axis. In so doing, X-Y control device 101 moves substrate 40 (shown inFIGS. 2A through 3B) along a plane that is located at a fixed distancefrom three-way beam splitter 25 (shown in FIGS. 2A and 2B) to verticallyalign specially treated portions of substrate 40 (e.g., solar cell 42)with three-way beam splitter 25. In one embodiment, the light 25 a isblocked by a shutter (not shown) while the substrate 40 is moved to testeach of the solar cells 42. Blocking the light 25 a during movement ofarticulation platform 96 may serve to minimize heating of the substrate40 and to also increase the accuracy of the data because the light 25 ais only shone onto the solar cells 42 at one similar location on thecells 42 for each of the cells 42.

FIG. 4B, with reference to FIGS. 1 through 4A and 6, illustrates a blockdiagram of a multi-pin combinatorial characterization apparatusaccording to an embodiment herein. As shown in FIG. 4B, multi-pincombinatorial characterization apparatus 5 a includes a lamp 122, light125 (emitted from lamp 122), substrate 40, probes 145, switching matrix150, programmable switch box 155, and computing device 70. Substrate 40,according to one embodiment, includes glass 133, a transparentconducting oxide (TCO) coating 135, electrodes 140 a, 140 b, and solarcell 42. Also shown in the embodiment of FIG. 4B, the electrodes (e.g.,electrodes 140 a, 140 b) are transferred to a back surface (e.g., TCO135) of substrate 40 where substrate 40 is not exposed to light (e.g.,light 125 emitted from lamp 122). In the embodiment shown in FIG. 4B,each solar cell 42 of substrate 40 can be processed under varied wet(e.g. texturing) or dry (electrode sputtering, absorb layer deposition)conditions during the combinatorial processing (e.g., primary screening(110), shown in FIG. 1). In the embodiment shown in FIG. 4B, the areainside solar cell 42 includes a positive electrode 140 a while the areaoutside of solar cell 42 is connected to a common electrical ground(e.g., electrode 140 b). According to one embodiment herein, electrodes140 a, 140 b are formed by chemical vapor deposition (CVD) and isolatedby a light scribing process on substrate 40.

In addition, as shown in FIG. 4B, electrodes 140 a, 140 b are connectedto a selective circuit (e.g., switching matrix 150). In one embodimentherein, a connection between electrodes 140 a and 140 b is made throughswitching matrix 150, which is designed to match the geometry ofsubstrate 40 with at least one probe 145 touching the inside of eachsolar cell 42 (e.g., using electrode 140 a) and the other touching thenearby outside of each solar cell 42 (e.g., using electrode 140 b). Forexample, switching matrix 150 may include a plurality of probes 145,where each probe 145 includes a spring load pin (e.g., pin 113 shown inFIG. 4A) used for better contact and reduced series resistance. Inaddition, substrate 40 is seated on a substrate support structure 150 aand may include, for example, articulation platform 96 shown in FIG. 2Band held in place by vacuum or by mechanical means, such as a clamp 84,or a combination of both. With a computing device 70 operativelyconnected to a selective circuit (e.g., as defined by the contacts madeby electrode 140 a and 140 b on substrate 40), a control program (e.g.,as stored and executed by a computing device 70, shown in FIG. 6)automatically selects one site (e.g., solar cell 42) on substrate 40 fortesting and may continue in series with the next site (e.g., anothersolar cell 42) until all the sites on substrate 40 are tested.

FIG. 4C, with reference to FIGS. 1 through 4B and 6, illustrates a blockdiagram of a Z-stage combinatorial characterization apparatus 5 baccording to an embodiment herein. As shown in FIG. 4C, Z-stagecombinatorial characterization apparatus 5 b includes a lamp 122, light125 (emitted from lamp 122), substrate 40, probes 145, Z-Stage device160, and computing device 70. Z-stage combinatorial characterizationapparatus 5 b also includes an X-Y stage 150 b (e.g., articulationplatform 96) that moves along a plane defined by an X-axis and a Y-axis(e.g., as indicated in FIG. 4A). As described above, substrate 40,according to one embodiment, includes glass 133, a transparentconducting oxide (TCO) coating 135, electrodes 140 a, 140 b, and a solarcell 42. In the embodiment of FIG. 4C, all the electrodes (e.g.,electrodes 140 a, 140 b) are transferred to a back surface (e.g., TCO135) of substrate 40 where substrate 40 is not exposed to light (e.g.,light 125, emitted from lamp 122). In the embodiment shown in FIG. 4C,each solar cell 42 of substrate 40 can be processed under varied wet(e.g. texturing) or dry (electrode sputtering, absorb layer deposition)conditions during the combinatorial processing (e.g., primary screening(110), shown in FIG. 1). In the embodiment shown in FIG. 4C, the areainside of solar cell 42 includes a positive electrode 140 a while thearea outside of solar cell 42 is the common electrical ground (e.g.,electrode 140 b). According to one embodiment herein, electrodes 140 a,140 b are formed by CVD and isolated by a light scribing process onsubstrate 40.

In addition, as shown in FIG. 4C, electrodes 140 a, 140 b are connectedto a selective circuit (e.g., Z-stage device 160). In one embodimentherein, a connection between electrodes 140 a and 140 b is made throughZ-stage device 160, which includes a plurality of probes 145 (e.g., twoprobes 145 are shown in FIG. 4C) where at least one probe 145 touchesthe inside of each solar cell 42 (e.g., electrode 140 a) and anotherprobe 145 touches the nearby outside of each solar cell 42 (e.g.,electrode 140 b). In addition, as above, X-Y stage 150 b and substrate40 can be held together by vacuum or by mechanical means, such as aclamp 84, or a combination of both. With computing device 70 operativelyconnected to a selective circuit (e.g., as defined by the contacts madeby electrode 140 a and 140 b on substrate 40), a control program (e.g.,as stored and executed by computing device 70 shown in FIG. 6)automatically selects one region (e.g., solar cell 42) on substrate 40for testing and may continue in series with the next site (i.e., solarcell 42) until all the sites on substrate 40 are tested.

In FIG. 4C, instead of the geometry-matched switching matrix 150 ofmulti-pin combinatorial characterization apparatus 5 a shown in FIG. 4B,only two probes 145 attached to Z-stage device 160 are used with oneprobe 145 touching the area inside of the solar cell 42 and the otherprobe 145 contacting the area outside of the solar cell 42. Substrate 40is also mounted on X-Y stage 150 b for movement along an X-Y plane (incontrast to the stationary substrate support structure of multi-pincombinatorial characterization apparatus 5 a shown in FIG. 4B) andprobes 145 are fixed onto Z-stage device 160 to provide movement along aZ plane. After finishing testing solar cell 42, Z-stage device 160lowers probes 145 to disconnect probes from electrodes 140 a, 140 b.Substrate 40 is then moved to the next site (as above) using X-Y stage150 b and the connection to electrodes 140 a, 140 b is restored (asshown in the sequential diagram in FIG. 4D).

The multi-pin combinatorial characterization apparatus 5 a shown in FIG.4B may be used for parallel testing. The Z-stage combinatorialcharacterization apparatus 5 b shown in FIG. 4C also has goodsite-to-site repeatability because the light 125 (e.g., emitted fromlamp 122) is fixed. These embodiments may also be universal for any kindof test substrate 40 and no specific fixture is required, particularlyfor the Z-stage combinatorial characterization apparatus 5 b shown inFIG. 4C. Besides the automation, multi-pin combinatorialcharacterization apparatus 5 a can also significantly increasethroughput by enabling parallel testing. FIG. 4E, with reference toFIGS. 1 through 4D, illustrates a schematic top view diagram of a probefixture 165 according to an embodiment herein. FIG. 4E shows that probefixture 165 includes pins 113, which are used during the IQE and EQEtest of solar cells 42 residing on substrate 40 (as described above). Asshown in FIG. 4E, according to embodiments herein, simultaneous IQE andEQE testing can be automated and the solar cells 42 of a test substrate40 may be tested in parallel. Consequently, the embodiments hereinincrease throughput on characterization significantly over theconventional methods where an operator is manually required to measureeach sample.

In addition, a characterization tool based on multi-pin combinatorialcharacterization apparatus 5 a or Z-stage combinatorial characterizationapparatus 5 b can optionally measure the temperature of solar cell 42currently being measured, and correct for any temperature increase thatoccurs (e.g., due to expose of light 125 from lamp 122) of substrate 40.Alternatively, substrate 40 may be cooled during the characterization ofthe solar cell 42 to maintain a steady temperature during eachmeasurement. For example, in one embodiment, a heat sink (not shown) maybe used to cool substrate 40. In yet another alternate embodiment,substrate 40 can be pre-heated to a temperature sufficient to mitigateany ancillary heating, caused by the lamp 122 used during the IQE andEQE measurements, insignificant.

Specially treated portions of substrate 40 (e.g., solar cell 42) mayinclude portions prepared using combinatorial processing. Combinatorialprocessing provides rapid evaluation of solar processing operations andmaterials. Some exemplary solar processing operations include, forexample, operations for adding (depositions) and removing layers(etching), defining features, preparing layers (e.g., cleans), doping,etc. In such an embodiment, the systems supporting the combinatorialprocessing are flexible to accommodate the demands for running thedifferent processes either in parallel, serial or some combination ofthe two. It is to be understood that the embodiments herein are notlimited to the combinatorial development and testing of solar cells 42,but may also be used to test electrochromic materials, photochromicmaterials, thermochromic materials, etc.

As used herein, combinatorial processing may include any processing(e.g., solar cell processing) that varies the processing conditions intwo or more regions of a substrate 40. A substrate 40 may be, forexample, a silicon substrate 40 such as a coupon that is used in solarprocessing. A region of a substrate 40 may be any portion of thesubstrate 40 that is somehow defined, for example by dividing thesubstrate 40 into regions having predetermined dimensions or by usingphysical barriers, such as sleeves, over the substrate 40. The regionmay or may not be isolated from other regions. For example, a substrate40 may be divided into two or more regions, each of which may or may notinclude solar cell structures 42 (e.g., Cu₂ZnSnS₄ solar cell structuresand copper indium gallium selenide solar cell structures may occupyseparate regions).

A process may be performed at each of the regions. For example, a firstregion is cleaned using a first cleaning agent, and a second region iscleaned using a second cleaning agent. The efficacies of the twocleaning agents are evaluated, and none, one, or both of the cleaningagents may be selected as suitable candidates for larger scaleprocessing (e.g., on regions with structures, or regions enabling moresophisticated testing, or a full substrate, etc.). According to otherexamples, multiple iterations of the same experiment are performed onthe same substrate 40, and any number of regions may be defined. Forexample, five cleaning solutions may be tested using fifteen regions ofa substrate 40, each cleaning solution being tested three times.

FIG. 5, with reference to FIGS. 1 through 4E, illustrates a flow diagramaccording to an embodiment herein. Step (170) of the method of FIG. 5provides a solar cell 42 that may be within a substrate 40 formeasurement (e.g., using quantum efficiency measurement tool 80 shown inFIG. 2B). Step (175) aligns a solar cell 42 (e.g., using X-Y controldevice 101 shown in FIG. 4A) beneath the measurement apparatus (e.g.,quantum efficiency measurement tool 80 shown in FIG. 2B). Next, step(180) applies a tuned wavelength of light 25 a (e.g., using emitter 92shown in FIG. 2B) to the aligned solar cell 42 on a substrate 40 thatincludes at least one solar cell 42 (as shown in FIGS. 2A and 2B). Step(185) of the method shown in FIG. 5 then simultaneously measuresabsorbed (e.g., light 25 a, as absorbed by solar cell 42 on substrate40, and measured using source meter 55 shown in FIG. 2A) and reflectedlight (e.g., light 40 a, reflected from solar cell 42 and passingthrough three-way beam splitter 25 to become light 40 b and detectedusing reflectance detector 30 shown in FIG. 2A) to calculate an IQE andEQE measurement (e.g., using computing device 70 shown in FIGS. 2A and6) therefrom.

A representative hardware environment for practicing the embodimentsherein is depicted in FIG. 6. This schematic drawing illustrates ahardware configuration of an information handling/computer system (e.g.,computing device 70 of FIG. 2A) in accordance with the embodimentsherein. The system comprises at least one processor or centralprocessing unit (CPU) 210. The CPUs 210 are interconnected via systembus 212 to various devices such as a random access memory (RAM) 214,read-only memory (ROM) 216, and an input/output (I/O) adapter 218. TheI/O adapter 218 can connect to peripheral devices, such as disk units211 and tape drives 213, or other program storage devices that arereadable by the system. The system can read the inventive instructionson the program storage devices and follow these instructions to executethe methodology of the embodiments herein. The system further includes auser interface adapter 219 that connects a keyboard 215, mouse 217,speaker 224, microphone 222, and/or other user interface devices such asa touch screen device (not shown) to the bus 212 to gather user input.Additionally, a communication adapter 220 connects the bus 212 to a dataprocessing network 225, and a display adapter 221 connects the bus 212to a display device 223 which may be embodied as an output device suchas a monitor, printer, or transmitter, for example.

Embodiments herein provide a measurement tool 80 that permits a sample(e.g., as prepared using combinatorial processes) to be loaded once andall other testing functions in association with internal quantumefficiency measurement and external quantum efficiency measurement to beautomated. In addition, such automation provides greater efficiency(e.g., less time to conduct the measurements because both the internalquantum efficiency measurement and external quantum efficiencymeasurement are performed simultaneously) over conventional systems,which would be advantageous for any research and development but may beof particular value in improving the throughput for combinatorialtesting. The speed at which the solar cells 42 are characterized isvaluable in achieving high performance combinatorial processing.Embodiments herein also provide greater precision (e.g., taking areference measurement simultaneous to take the measurement of theinternal quantum efficiency and external quantum efficiency) and greateraccuracy (e.g., reducing noise in the measurement through a lock-inamplifier 65).

One embodiment of the combinatorial screening process described above(e.g., FIG. 1) enables multiple experiments to be performed on a singlesubstrate 40 and the rapid evaluation of solar cell processingoperations and solar cell materials. Multiple solar cells 42 may resideon a singe substrate 40 and are designed to run the differentcombinatorial processes either in parallel, serial, or some combinationof the two. For example, embodiments herein allow forming differenttypes of thin film solar cells, CZTS solar cells, CIGS solar cells, andcadmium telluride (CdTe) solar cells that can be combinatorially variedand evaluated. These methodologies all incorporate the formation ofsite-isolated regions using a combinatorial processing tool and the useof these site-isolated regions to form the solar cell area. Therefore,multiple solar cells 42 may be rapidly formed on a single substrate 40for use in combinatorial methodologies. Any of the individual processesof the methods described herein may be varied combinatorially to testvaried process conditions or materials.

The use of combinatorial-based rapid device prototyping methods (e.g.,as shown in FIG. 1) permits fabrication, comprehensive characterization,and analysis of hundreds of unique solar cells 42 on a weekly basis todramatically increase learning rates. Alternative device structures,process integration schemes, and material compositions aresystematically explored at speeds that would otherwise be impossibleusing traditional methods and tools. This pace of development applied toEarth-abundant TFPV devices may represent an order of magnitudeacceleration of R&D in this area.

For example, CZTS is a compound semiconductor that evolves from thechalcopyrite structured I-III-VI2 compound CIGS, where indium/gallium issubstituted by zinc/tin and selenium by sulfur. The substituted elementsin CZTS are comparatively orders of magnitude more abundant than CIGSelements. CZTS has a band gap between approximately 1.45 and 1.6 eV,which is very close to the optimum value of an absorber layer of a solarcell 42. Additionally, the band edge absorption coefficient of CZTS isabove 1×10⁴ cm⁻¹ which enables its use as a thin film solar cellabsorber candidate.

A standard CZTS device structure may include the deposition of fourprimary layers on a substrate: a back contact (e.g., Mo), an absorberlayer (e.g., CZTS), a buffer layer (e.g., CdS or ZnS), and a frontcontact (e.g., ITO or Al:ZnO). Each material and deposition processprovides an opportunity to reduce manufacturing costs and increase cellefficiencies by using the combinatorial process described herein.Moreover, the similarity in process flow relative to current CIGSprocesses offers the intriguing possibility of retrofitting legacyproduction assets to produce lower cost devices using moreenvironmentally friendly, Earth-abundant materials.

Various techniques can be used for depositing the CZTS absorber layer,which is the most critical layer in the device stack. These techniquesinclude electron beam deposition continued by sulfurization, hybridsputtering, vacuum evaporation with sulfurization, sol-gel followed byH₂Se annealing, pulsed laser deposition, sputtering followed bysulfurization, single step RF sputtering, electroplating, and spraypyrolysis.

As described above, the embodiments herein improve the combinatorialscreening and the characterization of compounds (e.g., CIGS absorptionlayers, CZTS absorption layers, and other chalcopyrite structuredI-III-VI2 compound CIGS absorption layers) after the application ofthose formulations. For example, during an initial screening (e.g.,primary screening process ((110)) shown in FIG. 1), many samples (e.g.,18 spots or 46 spots on a single wafer, where each spot is a uniquematerial composition) are created using blanket films (e.g., as suppliedby Advantiv Technologies, Inc. Fremont Calif., USA) and thereaftertested. This initial screening (e.g., primary screening process (110))may have a simple criteria (e.g., maximizing external/internal quantumefficiency for a narrow wavelength band) to allow a quick evaluation andthereby quickly rule out materials that will not undergo the secondstage of testing (e.g., in secondary screening process ((120)) shown inFIG. 1). During the secondary screening process ((120)) shown in FIG. 1,a variety of more specific characterization methods may be performed onthe test cleaning formulations identified in primary screening process((110)) on fabricated patterned/metallized surfaces. Suchcharacterization methods include parametric tests and reliability tests.Sample criteria to evaluate include, but are not limited to: maximizingcurrent density, maximizing external/internal quantum efficiency for anarrow wavelength band, and maximizing external/internal quantumefficiency for the bandwidth of sunlight.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the embodiments herein that others can, byapplying current knowledge, readily modify and/or adapt for variousapplications such specific embodiments without departing from thegeneric concept, and, therefore, such adaptations and modificationsshould and are intended to be comprehended within the meaning and rangeof equivalents of the disclosed embodiments. It is to be understood thatthe phraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of several embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of the appendedclaims.

1. An apparatus for measuring quantum efficiency of a solar cell, saidapparatus comprising: an emitter that emits light; a three-way beamsplitter operatively coupled to said emitter, wherein said three-waybeam splitter splits said light into solar cell light and referencelight, and wherein said solar cell light strikes said solar cell; areference detector operatively coupled to said three-way beam splitter,wherein said reference detector detects said reference light; areflectance detector operatively coupled to said three-way beamsplitter, wherein said reflectance detector detects reflectance light,and wherein said reflectance light comprises a portion of said solarcell light reflected off said solar cell; a source meter operativelycoupled to said solar cell; a multiplexer operatively coupled to saidsolar cell, said reference detector, and said reflectance detector; anda computing device operatively coupled to said multiplexer, wherein saidcomputing device simultaneously computes an internal quantum efficiencyand an external quantum efficiency of said solar cell.
 2. The apparatusof claim 1, wherein said emitter comprises at least one of a quartztungsten halogen lamp, a filter wheel, an optical chopper, and amonochromator, and wherein said filter wheel isolates a specificbandwidth of said light.
 3. The apparatus of claim 1, further comprisinga lock-in amplifier operatively coupled to said multiplexer and saidcomputing device, wherein said lock-in amplifier extracts and amplifiessaid specific bandwidth from an output produced by said multiplexer. 4.The apparatus of claim 1, further comprising a white light biasedcontroller operatively coupled to said solar cell.
 5. The apparatus ofclaim 1, wherein said emitter comprises a laser that emits said lightwithin a specific bandwidth.
 6. The apparatus of claim 1, wherein saidsource meter measures a current from said solar cell.
 7. A system forsimultaneously measuring quantum efficiency, said system comprising: asolar cell; an emitter that emits light; a three-way beam splitteroperatively coupled to said emitter, wherein said three-way beamsplitter splits said light into solar cell light and reference light,and wherein said solar cell light strikes said solar cell; a sample trayoperatively coupled to said solar cell and positioned at a distance fromsaid three-way beam splitter; a multi-axis control device operativelycoupled to said sample tray, wherein said multi-axis control devicecontrols said sample tray along a plane parallel to said sample tray; areference detector operatively coupled to said three-way beam splitter,wherein said reference detector detects said reference light; areflectance detector operatively coupled to said three-way beamsplitter, wherein said reflectance detector detects reflectance light,and wherein said reflectance light comprises a portion of solar celllight reflected off said solar cell; a source meter operatively coupledto said solar cell, wherein said source meter measures a current fromsaid solar cell; a multiplexer operatively coupled to said solar cell,said reference detector, and said reflectance detector; and a computingdevice operatively coupled to said multiplexer, wherein said computingdevice receives measurement data from said multiplexer andsimultaneously computes an internal quantum efficiency and an externalquantum efficiency of said solar cell.
 8. The system of claim 7, whereinsaid multi-axis control device comprises: an X-axis articulator; anX-axis controller coupled to said X-axis articulator; a Y-axisarticulator; and a Y-axis controller operatively coupled to said X-axiscontroller and said Y-axis articulator.
 9. The system of claim 8,wherein said multi-axis control device controls said sample tray andaligns said solar cell proximate to said three-way beam splitter. 10.The system of claim 8, further comprising: a first remote controlleroperatively coupled to said X-axis controller, wherein said first remotecontroller controls said X-axis controller; and a second remotecontroller operatively coupled to said Y-axis controller, wherein saidsecond remote controller controls said Y-axis controller
 11. The systemof claim 7, wherein said internal quantum efficiency is calculated fromsaid measured current and said external quantum efficiency is calculatedfrom the detection of said reflectance light.
 12. The system of claim 7,further comprising: an articulation platform; and a clamp that securessaid solar cell to said articulation platform.
 13. The system of claim12, wherein said clamp is secured to said sample tray through a vacuumcreated by a channel operatively incorporated into said sample tray. 14.The system of claim 7, wherein said emitter comprises at least one of aquartz tungsten halogen lamp, a filter wheel, an optical chopper, and amonochromator.
 15. The system of claim 14, wherein said filter wheelisolates a specific bandwidth of said light.
 16. The system of claim 15,further comprising a lock-in amplifier operatively coupled to saidmultiplexer and said computing device, wherein said lock-in amplifierextracts and amplifies said specific bandwidth from an output producedby said multiplexer.
 17. A method measuring quantum efficiency, saidmethod comprising: providing a solar cell for measurement by placingsaid solar cell on a sample tray adjacent to a quantum efficiencymeasurement apparatus; emitting light from an emitter; splitting saidlight into solar cell light and reference light wherein said solar celllight strikes said solar cell; detecting reflectance light, wherein saidreflectance light comprises a portion of said solar cell light reflectedoff said solar cell; measuring a current from said solar cell; andsimultaneously computing an internal quantum efficiency and an externalquantum efficiency of said solar cell, wherein said internal quantumefficiency is calculated from the measured current and said externalquantum efficiency is calculated from the detection of said reflectancelight.
 18. The method of claim 17, further comprising detecting saidreference light, wherein said computing said internal quantum efficiencyand said external quantum efficiency comprises calculating saidreference light as a reference to detect any drift between saidreference and any of said light and said solar cell light.
 19. Themethod of claim 17, further comprising extracting and amplifying aspecific bandwidth of at least one of said light, said solar cell light,and said reflectance light.
 20. The method of claim 17, wherein saidsample tray automatically moves said solar cell on a horizontal planeadjacent to said quantum efficiency measurement apparatus to verticallyalign said solar cell with said quantum efficiency measurementapparatus.